Photodissociation of Charge Tagged Peptides

Abstract

Tris(2,4,6-trimethoxyphenyl) phosphonium acetyl (TMPP-Ac) was previously introduced to improve the mass spectrometric sequence analysis of peptides by fixing a permanent charge at the N-termini. However, peptides containing arginine residues did not fragment efficiently after TMPP-Ac modification. In this work, we combine charge derivatization with photodissociation. The fragmentation of TMPP-derivatized peptides is greatly improved and a series of N-terminal fragments is generated with complete sequence information. Arginine has a special effect on the fragmentation of the TMPP tagged peptides when it is the N-terminal peptide residue. Theoretical and experimental results suggest that this is due to hydrogen transfer from the charged N-terminus to the hydrogen-deficient peptide sequence.

Distinguishing Aspartic and Isoaspartic Acids in Peptides by Several Mass Spectrometric Fragmentation Methods

“…The mass spectra displayed in Figures 3a and b contain relatively few fragment ions. The most intense ion, b 7 +H 2 O, results from the carboxylic acid at the C-terminus interacting with the backbone to release the terminal amino acid [34, 42]. The intense b 4 ions in both spectra are from the D-effect.…”

“…Charge tagging with TMPP at the N-terminus of peptides was performed as described by He et al [42]. A molar ratio of approximately 1:10 of peptides to TMPP reagent was used in a total volume of 100 μL of 0.2 M NaHCO 3 at pH 9 with 20% acetonitrile.…”

“…Charge tagging has been shown to improve the b+H 2 O intensity in electrospray ionization (ESI) studies [24]. While previous charge tagging studies with PSD demonstrated very little fragmentation of these derivatized peptides due to the absence of a mobile proton, 157 nm photodissociation yields extensive sequence coverage [42]. …”

Charge Transfer Dissociation (CTD) Mass Spectrometry of Peptide Cations Using Kiloelectronvolt Helium Cations

“…Oftentimes, CID does not provide complete fragmentation of the peptide backbone and results in significant side-chain losses, including the loss of post-translational modifications, and thereby complicates the interpretation of tandem mass spectra [4,5]. These limitations have fueled a significant investment in alternative fragmentation techniques, including electron transfer dissociation (ETD) with cationic [6][7][8][9] or anionic [6,10] precursor ions, electron capture dissociation (ECD) with cationic [9,11], or anionic precursor ions [12], photodissociation [13][14][15][16][17][18][19][20], metastable atom-activated dissociation (MAD) [21][22][23][24][25][26][27][28], electron ionization dissociation (EID) [29], and electron detachment dissociation (EDD) [30]. Each technique has its merits and limitations.…”

“…Each technique has its merits and limitations. Photodissociation techniques require a chromophore that can absorb at the incident wavelength to initiate fragmentation, and such chromophores can be relatively nonselective amide bonds [13][14][15][16][17][18][19][20] or highly site-selective [31][32][33]. Chromophores can also include specific and native chromophores like disulfide bonds [34] but non-native chromophores are dependent on the ability to chemically modify the peptides or proteins of interest.…”